Let’s say I have a stopwatch and have marked out 8’ along my straight track. What is the formula to calculate the speed of a train if it takes so many seconds to get through that 8’? What if I had 80’ all the way around my layout on a mainline and clocked the time it takes for an engine to get around that entire route? Thanks for the help I know I am going to get from all you scientific minds out there. BTW I am in N SCALE!
HO is 1/87 scale so a mile is going to be 1/87 of a real mile or 5280’. So 5280/87=60.69’ or 60’ 8.25". Now comes the hard part to some extent in real time a train would cover one mile in 60 seconds at 60 miles per hour. For all practical purposes a scale mile can be rounded off to 60’ so a train travelling 60 mph in HO is going to cover one foot per second in real time. If you are using a differnt scale just substitute the scale in the first step.
from Subllime to Simple:
There are solid-state speedometers (like $40) that neasure speed each time around.
OR You can lay a 12" ruler alongside the track, and adjust speed to 1 second = 60 mph, 2 sec. = 30mph, and 1/2 sec. = 120 mph (a common speed for newbies). Stop watch, anyone?
There was once a state of the art throttle ($900) that included that feature.
ALL use a precribed distance: Feet per second / miles per hour, with a timer. So do Police Airplanes.
I found this page very helpful. Scroll down a little to find the speed calculator, it’s pretty big. 
If the link doesn’t work just hilite it, copy and paste it into your web browser and Waa Laaa!
I’m in HO and use 1 foot per second as equal to 60mph in real life. N scale it would be 6 inches per second for about 55mph in real life if I figure right.
I have a full explanation on my website http://www.xdford.digitalzones.com/modelrr10.htm of how to time the inches over 5 seconds for a number of scales including N.
I use “survery pegs” spaced at 5 inches in HO ( It would be 2.75 inches in N") and count each inch as miles per hour… the fuller explanation is on the web site.
Regards from Down Under
Trevor
The formula, which you use in a spreadsheet make up a speed table, is as follows:
(D/T) * 3600/5280 * S = smph
Where D is the distance measured off (in your example, 8), in actual feet
T is the time the train takes to cover the distance in seconds
S is the scale factor - for N, 160; for HO 87.1, for O, 48; etc.
I have an Excel spreadsheet which I will be happy to email to anyone who needs it - all you have to do to use it is to enter the distance you want to cover, and the scale (N, HO, O, S, Z, TT, or Q). It will produce a table for all times from 0.1 to 24.9 seconds. The times are adjustable, as well, if you know just a bit about spreadsheets. BTW, just for those who are “winging it”, the speed of an HO train which covers 3 feet in 3 seconds is actually 59.39 smph, not 60, and an N-scale train covering the same distance would take approx. 5.455 seconds if traveling 60 smph.
I also, many years ago wrote a small QuickBasic program to automatically calculate the speed of the train over a measured course, by measuring the time between two keystrokes, and pre-entering the scale and the distance to be covered. I can send it along as well, but you must supply your own copy of the QuickBasic interpreter. And your computer has to be in the train room, of course - the best bet nowadays is a laptop.
I would be happy to send either to anyone who wants them - email me, off-forum.
&nbs
I take one step more.
My clock runs 1:5, so I take the calculated miles by 5 and get scale miles. This gives a more realistic value.
And now you can go backwards.
Your train runs 5 scale miles with 60 miles per hour. It should take 12 minutes. This way I get the times for the schedule.
Wolfgang
The longer “sample” you have - the longer space you measure - the more accurate your timings will be. In N a scale mile is 33 ft., if your mainline is one scale mile or longer you can determine the start and end points of the scale mile and measure how long it takes a train to go that distance. If it takes one minute, the train’s going 60 MPH. Two minutes = 30 MPH. (Twice the time = half the speed.)
Hey, I appreciate your reply and since I am into computer stuff and excel spreadsheets, I would appreciate your emailing your formula. Send to omylip@earthlink.net and be sure to put in a subject line so it doesn’t get trashed in my spam box. I looked up a couple of the other suggestions and they were great also but I couldn’t download them, just compute on the screen and print it out. I like your spreadsheet idea whereby I can put in any numbers that I want. Thanks a bunch in advance.
Ed
OP:
If you put your telegraph poles at some handy, whole-number spacing, such as 1 or 2 feet, you can calculate rough speeds at any point very easily. In fact, didn’t the old-time railroadmen do just that in real life?
With most QSI sound decoders (P2K, Atlas), you can hit F10 and the loco will give its scale speed if it is moving!
So, you measure real feet per second. A tape measure gives you real feet. Your stop watch give you seconds. You want to compute scale miles per hour from real feet per second. You have a hand calculator.
Multiply real feet by 160 to convert real feet to scale feet
Divide scale feet by 5280 to get scale miles.
Divide seconds by 3600 to get hours.
Then divide scale miles by hours and you have scale miles per hour.
I’d measure time over a longer distance to get a more accurate number. Your reaction time is about 3/4 of second, so your stop watch time may be off by that much. If the total elapsed time is only a couple of seconds, a 3/4 of a second reaction time will throw you off by quite a bit. If you run for 100 seconds then 3/4 second doesn’t matter much.
Aren’t we missing something here?
I don’t dispute the formulas or the scale conversions; I’m sure you guys are right, but I’m not sure that a straight mathematical equation is going to give a satisfactory answer. After all, we tend to use selective compression when modelling scenes, so the assumption that 60 feet of mainline equals one mile may be invalid. In fact, that sixty feet could be ten miles or more depending on what we’ve chosen to model.
I realize that this argument muddies the waters a bit, and goes beyond the simple question that was asked, but I can’t help thinking that one foot per second could seem awfully fast in the context of the surrounding scenery. For me, it’s more a question of what “looks right” than what the numbers are.
Just a thought.
Chris
What “looks right” is usually incredibly fast. Prototype switching is supposed to be at 5MPH. At that speed, a 40ft boxcar takes 6 full seconds to pass a point in space - regardless of scale. How many are willing to do their switching at that realistic speed? And note that the problem gets worse as the scale gets smaller.
To the eye, an 11" long O boxcar taking 6 seconds to pass the switchstand at a turnout is slow. Watching the same boxcar in HO (6" long) take 6 seconds to pass the switchstand is painful, I doubt many could stand to see the N scale boxcar (3.5") take 6 seconds to pass the switchstand.
Even today, very few trains run anywhere near a sustained 60MPH. And they certainly didn’t in the era I model (1900). Narrow gauge lines very seldom saw more than 35MPH, and 25 MPH was probably closer to the norm. A Climax or Shay had a top speed of 12 MPH.
Because it seems so slow to operate at scale speeds, being able to know the scale speed becomes the ticket to more realistic operatio
Well…the thing is that what you’re getting into involves so-called “scale time” in a way. Frank Ellison suggested that since we do things quicker than a real railroad could in terms of switching etc, and had less distance to cover, that we should use “scale time” (which later was called “fast time”) so that each real hour was considered say six “fast” hours. So if it took a train five real minutes to go from point A to point B, it would take 30 “fast” minutes. In that vein, he said you could also record distances using the same ratio, so if point A and point B were a scale mile apart, you would show them in the timetable as being six “smiles” (“Scale Miles”) apart.
However all of this is really theatrics to make the layout seem bigger, none of this actually affects scale distances or the speed of the trains!! A train going one scale mile from point A to point B at 30 MPH is going to take the same time (2 real minutes) to cover the same distance (1 scale mile) whether we call it six ‘smiles’ or
You can do all that math or you can check out this www.trainspeed.com
Excellent explanation, Stix, thanks. This makes a whole lot of sense.